1. Field of the Invention
The present invention relates to a recording system for use when digital data is recorded on a recording medium.
2. Related Background Art
As a system for encoding and recording data to be recorded, a system in which an input data series is converted into a Run Length Limited code (hereinafter, referred to as "RLL code") series and recorded in accordance with the NRZL (NRZ) rule has been disclosed in, for example, U.S. Pat. No. 4,860,324.
The NRZL rule refers to a system in which, for instance, when the RLL coded data is as shown in FIG. 1A, this data is converted into a signal as shown in FIG. 1B.
In the case of decoding, an interval between code 1 and code 1, that is, data between marks is decoded.
A recording medium generally has a reproducing characteristic such that response of reproduction output decreases at high frequencies as shown in FIG. 2. Therefore, when a pulse width of a recording signal is narrow, the response decreases.
The RLL codes are generally expressed as d, k, m, and n codes.
In this case, m denotes the number of bits constituting one block of the input data series and n indicates the number of bits of one block of the input data series, after completion of the conversion, in the corresponding RLL code. On the other hand, d represents the minimum number of continuous code bits "0" which is permitted in the RLL codes. When d.gtoreq.1, the code bit "1" is not permitted to occur twice in immediate succession. k indicates the maximum number of continuous code bits "0" which is permitted in the RLL code.
In the RLL codes, the case where the values of d and k, particularly the value of d, is relatively large will now be considered. As an example, the case of d=3 is shown in FIG. 3.
In this case, when a light source for recording is flickered and recorded on an optical recording medium in accordance with the NRZL rule, particularly, in the case of a high density and a short flickering time of the light source, there could occur such a situation that enough energy is not given to the recording medium and optical recording is not satisfactorily performed. This is because the surface of the medium is changed by the heat to effect the recording, and consequently some minimum irradiation time is needed to assure that recording has occurred.
FIG. 4 shows examples of a change in reproduction output in the case where a width T of recording time is large and a reproduction output in the case where it is small.
Therefore, in the conventional NRZL recording of the RLL codes, there are problems that when the illumination time of the light source is short, reproduction output of a sufficiently high level cannot be obtained and it is difficult to reduce errors of information. In other words, there is a problem that for a given error rate, it is difficult to improve the recording density.